1. Field of the Invention
This invention relates to a glass fiber composition that will withstand the high temperatures required for a fire-rated product such as an acoustical ceiling tile, wall insulation material, or an interior wall sheathing product. It is well known that conventional mineral fibers prepared by attenuating a molten stream of basalt, slag or other, vitreous mineral constituent can be formulated to withstand melting at temperatures of about 1500.degree. F. (815.degree. C.). In addition, special additives can be incorporated into glass fibers to increase their melting point, but these special glass fibers are very expensive. Even mineral wool products may exhibit some softening distortion and shrinkage as temperatures approach 1500.degree. F. (815.degree. C.). Clay fillers, e.g. kaolin clay, are frequently incorporated in mineral wool products to improve their fire resistance.
Conventional glass fibers have a nominal "softening point" of about 1000.degree. F. (about 538.degree. C.) and are generally considered to be unsuitable for formulating firerated products. It has now been discovered that the incorporation of calcium carbonate (limestone) or calcium magnesium carbonate (dolostone) in combination with a halogenated resin binder causes a reaction with the surface of the glass fibers at high temperatures which increases the resistance of the glass fibers to high temperatures. Carbonate-containing glass fiber compositions have been formulated which are capable of passing the ASTM E-136 or the British Standard 476, Part 4 non-combustibility tests.
2. Description of the Prior Art
The water-felting of dilute aqueous dispersions of mineral wool is a well known process for manufacturing panel products such as acoustical ceiling tiles and wall insulation panels. In the process, a dispersion of mineral wool, a binder and other ingredients are flowed onto a moving foraminous wire screen, such as an Oliver or Fourdrinier mat forming machine, for dewatering. The wet mat is first dewatered by gravity and then vacuum suction is applied. The wet mat is dried in heated convection drying ovens, and the product is cut and, if desired, top coated with paint to produce structural panels for use as acoustical ceiling files or sheathing.
U.S. Pat. No. 5,134,179 discloses a composite fiberboard comprising inorganic fibers (mineral wool or glass fibers), perlite, clay and cellulosic fibers as the primary ingredients with a latex binder containing extender particles. Calcium carbonate and magnesium carbonate are disclosed as extender particles. The latex binder and extender particles are deposited upon the cellulosic fibers. There is no teaching in this patent that the products are fire-rated or that there is any reaction between the extender particles and the inorganic fibers. In fact, there are no operating examples disclosing the use of glass fibers.
U.S. Pat. No. 3,220,915 discloses glass fibers which have resistance to high temperature provided by several oxide ingredients, including calcium oxide, incorporated into the fiber-forming composition. The fibers produced from the melt are semi-crystalline and are resistant to high temperatures.
U.S. Pat. No. 3,248,257 discloses flame-resistant mineral fiber tiles prepared from slag wool wherein the fibers are treated with an aqueous chemical composition to provide a heat-resistant refractory coating on the fibers. Several chemicals may be used to provide the heat-resistant coating, however, there is no teaching that a carbonate can be used. The patent discloses that glass fibers are not very reactive with the chemical composition, and in fact, practically inert in the process of producing the treated tile. It further teaches that whether there is a reaction at red heat is not material to the invention.
U.S. Pat. No. 5,250,153 discloses a method for manufacturing a mineral wool panel wherein an anionic resin latex binder is deposited on the mineral fiber by means of a cationic flocculant. There is a disclosure that a limestone filler can be incorporated into the composition, however, there is no teaching that the limestone filler reacts with the mineral fiber to increase its fire resistance.
U.S. Pat. No. 4,611,445 discloses a ceiling panel resistant to sag when exposed to a fire comprising mineral wool fibers and lithium carbonate. The patent discloses that the devitrification action of the lithium carbonate is specific to mineral wool fibers. It also discloses that lithium carbonate in combination with glass fibers reduces the fusion and melting temperature resulting in earlier shrinkage.
U.S. Pat. No. 3,348,994 discloses a glass fiber board product which contains a silicate devitrifying agent and a devitrification accelerator (e.g. titania or magnesium carbonate). As stated in this patent, the invention is concerned with the use of asbestine or an equivalent silicate to cause relatively rapid devitrification of glass fibers.